Reconsideration of methods and standards: Digestion of diaper wipes and use of matrix-matched calibration standards for dust lead analysis

Diaper wipes are widely used for sampling residential dust for lead analysi s. A thicker type of diaper wipe was incompletely digested and had low reco veries (similar to 40%) of lead on stock solution spikes using existing pro tocols. A modified protocol was applied to various quality control samples prepared with thicker diaper wipes in 134 batches of field samples. Modific ations included a larger reagent volume (20 mt), more concentrated a cid (5 0% HNO3 foil owed by concentrated HNO3), 3 h on the hot plate, and squeezin g wipe residues during filtration. Seventeen hatches were reanalyzed using matrix-matched standards. Acceptable lead recoveries were obtained for stoc k solution spikes (88%) and spikes prepared with leaded dust-SRM 2582 (88%) , SRM 2589 (96%), and CRMO 14-050 (99%). Matrix-matched calibration standar ds increased mean lead recoveries by an additional 8%. Our protocol may pro vide a basis for a standard operational procedure for wipe digestion and an alysis. Differences in estimates of dust lead loadings attributable to the type of wipe and to sample preparation and calibration procedures have impl ications for risk assessment, clearance testing, and comparability of labor atory data. Reconsideration of current protocols for wipe materials, wipe d igestion, and judging laboratory performance (including the ELPAT external proficiency testing program for wipes) is warranted.